A Telescope

A Telescope’s Most Important Features

As I have indicated in the previous pages, magnification is probably the least important thing to consider when buying a telescope. One reason I say this is because it is possible to make ANY telescope have ANY magnification you want! Yes, I mean even a five dollar telescope with plastic lenses from a toy store! If you were to put a lot of magnification on such a modest telescope, you would only see featureless blobs of light. This fact is mainly due to the small size of the telescope’s biggest lens. Furthermore, you should know that some telescopes use a big magnifying mirror rather than a lens (more on this later). The biggest lens or mirror of a telescope is called the objective. All of the lenses and/or mirrors in a telescope are referred to as the telescope’s optics.

Rule #1 The size of a telescope’s objective is more important than magnification.

The reason why objective size is so important is because the objective is the part of the telescope which collects the light from the object you are viewing. The bigger the objective, the more light there is collected from the object you are viewing; therefore, the object appears brighter. For example, let us say that there are three different telescopes looking at the planet Jupiter at a magnification of 300 times (or 300x). The first instrument has an objective 2.4 inches in diameter, the second telescope’s objective is 4.5 inches in diameter, while the last sports a 6 inch diameter objective. The diameter of the telescope’s objective is called the aperture. Incidentally, 2.4 inches (or 60 millimeters) of aperture is the size of the typical department store 600x telescope.

In the smallest telescope, you would see the planet as a dim yellow disk where the largest cloud bands in its atmosphere are vaguely visible. Its famous Great Red Spot may be seen as a faint blob. The view is still interesting, especially to someone who hasn’t before seen Jupiter!

4.5 inches of aperture make the planet appear much brighter. The same cloud belts visible in the smallest scope are now sharply defined and are definitely colored dark brown. The Great Red Spot now has sharper outlines and is showing more red. Smaller cloud belts are also visible. A beautiful sight to be sure!

But the view through the telescope with 6 inches of aperture may be breathtaking! The disk of Jupiter is a brilliant yellow. Not only is color more pronounced in the large and small cloud belts, but swirls and eddies may also be visible. The Great Red Spot shows up easily against its surroundings.

Which brings us to Rule Number Two.